The present invention relates to a low temperature process for the production of hydrogen from methane or methane rich hydrocarbons and steam. More particularly the present invention relates to a low temperature process for the production of hydrogen from methane or methane rich hydrocarbons and steam using a group VIII metal oxide(s) containing solid catalysts in two parallel reactors. The present invention also particularly relates to a process for the continuous production of hydrogen from methane or methane rich hydrocarbons and steam at low temperature below 650xc2x0 C. using a group VIII metal oxide(s) containing solid catalyst in two parallel reactors operated in a cyclic mariner for the decomposition of methane or methane rich hydrocarbons to hydrogen and carbon, which is deposited on the catalyst, and for the gasification of the carbon deposited on the catalyst by steam in the presence or absence of oxygen.
The demand for hydrogen is increasing day by day for hydrotreating processes in petroleum industries and also for hydrogen fuel cells, both stationary and non-stationiary fuel cells. Since hydrogen is a non-polluting fuel, its use as a fuel particularly for fuel cells used in the automobile transport has been increasing very fast. However, hydrogen fuel cells require carbon monoxide free hydrogen as a fuel to avoid deactivation of the noble metal catalyst in the fuel cells.
The main natural sources of hydrogen are hydrocarbons and water. Amongst hydrocarbons, methane has the highest hydrogen to carbon ratio and is hence the most preferred choice amongst hydrocarbons for hydrogen conversion.
Conventional processes for the production of hydrogen are based on steam reforming of hydrocarbons, such as naphtha and methane or natural gas and autothermal reforming of hydrocarbons, particularly heavier hydrocarbons. Hydrogen production processes have been recently reviewed by Fierro and co-workers [Pena, M. A., Gomez, J. P., and Fierro, J. L. G., Applied Catalysis A. General, volume 144, page 7-57, 1996].
The prior art processes of hydrocarbon steam reforming and autothermal reforming are operated at high temperatures of over about 900xc2x0 C. and the product stream of these processes contains appreciable amounts of carbon monoxide along with hydrogen. The prior art processes also suffer from the disadvantage that removal of carbon monoxide at low concentrations from hydrogen is very expensive. The high cost factor involved in the separation of carbon monoxide from hydrogen and limitations of high temperature required for operation renders both prior art processes uneconomical for the production of carbon monoxide free hydrogen.
The prior art also discloses processes for the production of carbon monoxide free hydrogen from methane at low temperatures of below 600xc2x0 C. Recently, Kikuchi has described a process based on steam reforming of methane in a membrane reactor to produce hydrogen free of carbon monoxide (Kikuchi, E., Hydrogen permselective membrane reactors, CATTECH, March 1997, pages 67-74, Balzer Science Publishers). Kikuchi discloses the use of a Pd/ceramic composite membrane for steam reforming of methane over a commercial supported nickel catalyst at temperatures as low as 500xc2x0 C., to obtain methane conversion to carbon monoxide free hydrogen of upto 100%. The hydrogen produced in this process by the steam reforming of methane is continuously removed form the reaction system by the selective permeation of hydrogen through the Pd-membrane. However, this process suffers from the following limitations or drawbacks: 1) Because of the use of a number of Pd-membrane tubes, the capital costs are very high; 2) potential for the deactivation of the Pd-membrane due to the deposition of carbonaceous matter exists, 3) membrane stability is a problem; 4) there is a possibility of membrane failure due to the formation of pin holes in the membrane.
Japanese patent JP 09234372 A2 of Sep. 2, 1997 discloses a process for the manufacture of hydrogen by thermal decomposition of hydrocarbons at 200xc2x0 C.-1000xc2x0 C. using a catalyst containing nickel, alkali or alkaline earth compounds.
Russian patent RU 2071932 C1 of Jan. 20, 1997 discloses the production of hydrogen and carbon by the thermal decomposition of methane on nickel catalyst. Japanese patent JP 11228102 A2 discloses reactors for the thermal decomposition of methane to form carbon and hydrogen.
Hydrogen production by catalytic cracking of methane or natural gas and other hydrocarbons below 900xc2x0 C. is disclosed in a few publications [Zhang, T and Amiridis, M. D., Applied Catalysis A: General, Volume 167; pages 161-172, 1998; Muradov, N. Z. Energy Fuels, Volume 12, pages 41-48, 1998; Kuvshinov, G. G., et al, Hydrogen Energy Progress XI Proceedings of the World Hydrogen Energy Conference,. 11th, Volume 1, pages 655-660, edited by Veziroglu, T., 1996; Muradov, N. Z., Proceedings of US DOE Hydrogen Program Review, volume 1, page 513-535, 1996].
While the hydrogen produced in the above prior art processes, based on catalytic cracking or thermo-catalytic decomposition of methane and other hydrocarbons, is free from carbon monoxide and carbon dioxide, the rate of deactivation of the catalyst is high due to the carbon formed and deposited on the catalyst accompanied by an increase in the pressure drop across the catalyst bed. This makes the above processes unsuitable for hydrogen production on a commercial scale.
Choudhary and Goodman recently report a process for the production of carbon monoxide free hydrogen involving step wise methane stream reforming [Choudhary, T. V. and Goodman, D. W., Catalysis Letter, volume 59, page 93-94, 1999]. In this process, methane pulse and water pulses are alternately passed over a pre-reduced nickel based catalyst at 375xc2x0 C. When methane pulse is passed over the catalyst, the methane from the pulse decomposes to hydrogen en and carbon, leaving the carbon deposited on the catalyst. When the water pulse is passed over the catalyst with carbon deposited thereon, the carbon on the catalyst reacts with steam to form CO2, hydrogen and methane. In this process, although the carbon monoxide free hydrogen is produced by, the catalytic cracking of methane and the carbon deposited on the catalyst is removed by the cyclic operation of the methane and water pulses in the same reactor, the process is not operated in steady state and hydrogen production is not continuous. It is therefore not practical or economical to produce carbon monoxide free hydrogen on large scale by this transient process involving cyclic operation of the methane and water pulses.
In view of the above mentioned drawbacks and limitations of prior art processes, there is a pressing need to develop a continuous process for the production of carbon monoxide-free hydrogen by catalytic decomposition of methane or natural gas at low temperature of below 600xc2x0 C., thereby avoiding the carbon build up on the catalyst by its periodic removal.
It is an object of the invention to provide a low temperature process for the continuous production of hydrogen from methane or methane rich hydrocarbons and steam.
It is yet another object of the invention to provide a process for the continuous production of hydrogen from methane or methane rich hydrocarbons and steam that is cost effective.
It is a further object of the invention to provide a process for the continuous production of hydrogen that is carbon monoxide or carbon dioxide free and is useful as a fuel.
It is another object of the invention to provide a process for the production of hydrogen that is carbon monoxide or carbon dioxide free in while avoiding build up of carbon on the catalysts.
It is another object to provide a low temperature process for the continuous production of hydrogen from methane or methane rich hydrocarbons and steam that avoids the problem of high cost involved in the removal of carbon monoxide from hydrogen at low concentrations and is therefore cost effective.
Accordingly, the present invention provides a process for the continuous production of hydrogen from a feed comprising of methane and/or natural gas and/or methane rich hydrocarbons, and steam at low temperature using a solid catalyst comprising of group VIII metal oxide(s) in two parallel reactors, said process comprising:
i. reducing the solid catalyst in both the reactors by contacting the catalyst with a gaseous feed comprising a reducing agent at a concentration in the range of from 1 mole % to 100 mole %, at a gas hourly space velocity in the range of from 100 cm3gxe2x88x921hxe2x88x921 to about 100000 cm3gxe2x88x921hxe2x88x921 at a temperature in the range of from 350xc2x0 C. to 650xc2x0 C. and at a pressure of at least 1.0 atm. for a time period in the range of 0.1 hour to 100 hours;
ii. contacting a first gaseous feed comprising methane and/or natural gas and/or methane rich hydrocarbons called Feed A at a gas hourly space velocity in the range of from 50 cm3gxe2x88x921hxe2x88x921 to 50000 cm3gxe2x88x921hxe2x88x921 with the solid catalyst reduced in step i. above in a first reactor called Reactor A, at a temperature in the range of from 300xc2x0 C. to 650xc2x0 C. and at a pressure of about at least 1.0 atm., simultaneously contacting a second gaseous feed comprising steam called Feed B with the solid catalyst reduced in step i. above in a second reactor called Reactor B, at the same gas hourly space velocity, temperature and pressure as that employed in the said first reactor, while regularly switching over the said first feed and the said second feed between the two parallel reactors at a time interval of from 0.1 minute to 100 minutes, to obtain a mixed product stream comprising hydrogen from the two reactors.
In one embodiment of the invention, the two parallel reactors may be two parallel fluid bed reactors or two fixed bed reactors.
In a further embodiment of the invention, the two parallel reactors are two parallel fixed bed reactors.
In another embodiment of the invention, the said first feed and the said second feed are switched between the said first and second reactors by a two-flow switch valve operable manually or automatically.
In another embodiment of the invention, the Group VIII metal oxides are selected from oxides of Fe, Co, Ni, Ru, Rh, Pd, Pt, Ir and Os.
In another embodiment of the invention, hydrogen is formed in both the reactors, while carbon dioxide is formed in only one reactor.
In another embodiment of the invention, the reducing agent used in step i. of the invention is selected from the group consisting of hydrogen, carbon monoxide, or a mixture thereof.
In a further embodiment of the invention, the preferred reducing agent used in step i. of the invention is hydrogen.
In another embodiment of the invention, the preferred concentration of the reducing agent in the feed gas is in the range of from 5 mole % to 50 mole %, the preferred gas hourly space velocity is in the range of from 500 cm3gxe2x88x921hxe2x88x921 to 20000 cm3gxe2x88x921hxe2x88x921, the preferred temperature is in the range of from 400xc2x0 C. to 600xc2x0 C. and the preferred reduction period is in the range of from 1 hour to 20 hours.
In another embodiment of the invention, the preferred gas hourly space velocity in step ii. of the process for the first feed is in range of 200 cm3gxe2x88x921hxe2x88x921 to 20000 cm3gxe2x88x921hxe2x88x921 with the preferred temperature in the first reactor in the range of from 350xc2x0 C. to 600xc2x0 C., the preferred gas hourly space velocity for the second feed being in the range of 200 cm3gxe2x88x921hxe2x88x921 to 20000 cm3gxe2x88x921hxe2x88x921 with the preferred temperature in the second reactor being in the range of from 350xc2x0 C. to 600xc2x0 C., the preferred interval of time for the feed switch over being in the range of from 1 minute to 30 minute, the preferred concentration of methane in the first feed being in the range of 10 mole % to 100 mole %, the preferred concentration of ethane and higher alkanes in the first feed is in the range of from 0 mole % to 5 mole %; the preferred concentration of N2, He, Ar or their mixture in the first feed is in the range of from 0 mole % to 90 mole %, the preferred concentration of steam present in the second feed being in range of from 20 mole % to 100 mole %, the preferred concentration of oxygen in the second feed being in the range of 0 mole % to 5 mole %, the preferred concentration of N2, He, Ar or their mixture in the second feed is in the range of from 0 mole % to 80 mole % and the preferred group VII metal oxide in the solid catalyst is nickel oxide, cobalt oxide or iron oxide or any mixture thereof.
In a further embodiment of the invention, the solid catalyst used in the process of the invention is preferably selected from NiOxe2x80x94ZrO2, NiOxe2x80x94CoOxe2x80x94MgO, NiOxe2x80x94Fe2O3xe2x80x94ThO2, NiOxe2x80x94CeO2, NiOxe2x80x94Y2O3, NiO/Cexe2x80x94NaY Zeolite, NiO/H-beta zeolite, NiO/H-ZSM-5 zeolite, NiO/HM zeolite and NiO/Si-MCM-41 zeolite or a mixture of two or more thereof.
The two parallel reactors may be two parallel fluid bed reactors or two fixed bed reactors, preferably two parallel fixed bed reactors. The first feed and the second feed are switched between the first and second reactors by a two-flow switch valve operable manually or automatically. The Group VIII metal oxides are selected from oxides of Fe, Co, Ni, Ru, Rh, Pd, Pt, Ir and Os.
Hydrogen is formed in both the reactors, while carbon dioxide is formed in only one reactor. The reducing agent used in step i. of the invention is selected from hydrogen, carbon monoxide or a mixture thereof. The preferred reducing agent used in step i. of the invention is hydrogen.
The preferred concentration of the reducing agent in the feed gas is in the range of from 5 mole % to 50 mole %, the preferred gas hourly space velocity is in the range of from 500 cm3gxe2x88x921hxe2x88x921 to 20000 cm3gxe2x88x921hxe2x88x921, the preferred temperature is in the range of from 400xc2x0 C. to 600xc2x0 C. and the preferred reduction period is in the range of from 1 hour to 20 hours. The preferred gas hourly space velocity in step ii. of the process for the first feed is in range of 200 cm3gxe2x88x921hxe2x88x921 to 20000 cm3gxe2x88x921hxe2x88x921 with the preferred temperature in the first reactor in the range of from 350xc2x0 C. to 600xc2x0 C., the preferred gas hourly space velocity for the second feed being in the range of 200 cm3gxe2x88x921hxe2x88x921 to 20000 cm3gxe2x88x921hxe2x88x921 with the preferred temperature in the second reactor being in the range of from 350xc2x0 C. to 600xc2x0 C., the preferred interval of time for the feed switch over being in the range of from 1 minute to 30 minute, the preferred concentration of methane in the first feed being in the range of 10 mole % to 100 mole %, the preferred concentration of ethane and higher alkanes in the first feed is in the range of from 0 mole % to 5 mole %, the preferred concentration of N2, He, Ar or their mixture in the first feed is in the range of from 0 mole % to 90 mole %, the preferred concentration of steam present in the second feed being in range of from 20 mole % to 100 mole %, the preferred concentration of oxygen in the second feed being in the range of 0 mole % to 5 mole %, the preferred concentration of N2, He, Ar or their mixture in the second feed is in the range of from 0 mole % to 80 mole % and the preferred group VII metal oxide in the solid catalyst is nickel oxide, cobalt oxide or iron oxide or any mixture thereof.
In a feather embodiment of the invention, the solid catalyst used in the process of the invention is preferably selected from NiOxe2x80x94ZrO2, NiOxe2x80x94CoOxe2x80x94MgO, NiOxe2x80x94Fe2O3xe2x80x94ThO2, NiOxe2x80x94Ceo2, NiOxe2x80x94Y2O3, NiO/Cexe2x80x94NaY Zeolite, NiO/H-beta zeolite, NiO/H-ZSM-5 zeolite, NiO/HM zeolite and NiO/Si-MCM-41 zeolite or a mixture of two or more thereof.
The solid catalyst comprising group VIII metal oxide(s)used in the process of this invention can be prepared by the coprecipitation or impregnation catalyst preparation techniques known in the prior art.
The role of step-i of the process of this invention is to reduce the reducible metal oxide, for example nickel oxide, cobalt oxide, iron oxide, etc., present in the catalyst. This step is critical one; the reduction of group VIII metal oxide to its metallic form at least from the surface of the catalyst is essential for the catalytic activity in the process of this invention.
In step-ii of the process of this invention, the methane or methane-rich hydrocarbons, steam and oxygen are reactants, which are converted at least partly in the process. The role of steam is to react with the carbon, which is formed in the decomposition of methane on the reduced catalyst, producing carbon dioxide and hydrogen from the catalyst from time to time and thereby removing the carbon depositedon the catalyst. The role of the oxygen is to activate the carbon which is otherwise difficult to gasify by steam alone. The oxygen is consumed at least party by its reaction with the carbon to form CO2. Role of the solid catalyst is to catalyse the methane decomposition reaction and the carbon gasification by steam and oxygen.